Review some of the common plants toxic to horses and their effects

We have all seen that puddle of drool form under our horse’s mouth when he’s standing in the crossties. You might be aware this is caused by consumption of clover, but do you know a toxin called slaframine causes the hypersalivation? Slaframine commonly forms on red clover and irritates horses’ oral and gastrointestinal mucosa (the lining of these structures), causing the drool puddles we see. Although hypersalivation causes no significant threat to our horses, other common plants can have more sinister toxic effects.

Toxic Plants Horses Should Not Eat

Buttercups, for example, add a nice bit of color to the fields but contain the toxic compound ranunculin. This mild toxin generally only causes irritation to oral mucosa but, if a horse consumes it in large amounts, can affect the mucosa deeper in the intestinal tract. Horses that have eaten buttercups could exhibit clinical signs of colic or develop diarrhea. Unlike clover, buttercups are not particularly appetizing to horses and rarely cause problems despite their abundance.

Dock, a hearty weed, flourishes in harsh climates and overgrazed paddocks. It contains high levels of nitrates and oxalates, which are both toxic. When it comes to horses, our primary concern is the oxalates, which bind calcium and magnesium, affecting muscle contraction. Common clinical signs include muscle twitching and weakness, but the muscles at greatest risk are the diaphragm and heart. Oxalates will also concentrate over time in the kidneys, causing damage to renal tubules. Unlike some other toxic plants, dock maintains its toxic principles even when dried, so it is not considered safe in hay